In the dry-cleaning industry it is known to recover organic solvents by passing an airstream through a rotating drum or cage containing the load to be cleaned, the solvent-laden air then traversing an adsorber filled with a suitable mass such as activated charcoal. When the adsorption capacity of the mass has been reached, the airstream is switched to a previously inactive second adsorber while the first one is being regenerated with the aid of steam passing through the charcoal bed. Reference in this connection may be made to U.S. Pat. Nos. 2,777,534 and 2,910,137; a particularly advantageous adsorber is shown in commonly owned U.S. Pat. No. 3,955,946.
Because of the relative complexity and high cost of such adsorbers and their associated regenerating equipment, it is uneconomical to provide an individual solvent-recovery system of this type for each of several dry-cleaning machines or other treatment units of a single plant. If a single pair of alternately activated adsorbers is to serve a plurality of such units, conventional techniques therefore call for the use of adsorbers of sufficient capacity to handle the combined solvent volume from all these units if they happen to operate simultaneously. Since, however, the operating periods of such units are independent of one another, it may happen that an active adsorber must keep operating without pause during a succession of overlapping solvent-recovering periods of the several units. As the amount of circulating solvent varies with the number of units connected in parallel to the inlet of the active adsorber, there is no simple way of determining when the capacity of the adsorber is reached and a switchover to the previously regenerated alternate adsorber is to be carried out.